How often should I change my furnace filter? Are the expensive filters worth the money?

How often should I change my furnace filter? Are the expensive filters worth the money?

Dear Matt,
How often should I change my furnace filter? I have been trying to remember to do it every 30 days, but the filter looks clean. Am I just wasting a filter by doing it that frequently? Also, what type of filters should I be buying? Are the expensive filters worth the money?

My rule of thumb is if the filter looks dirty change it! I have read anywhere from every one to three months filters should be changed, but that also depends on how often your furnace ran and how dirty the filter looked when you checked it. It’s a good idea to at least check the filter every month, and if it is dirty go ahead and swap it with a new one. 

Dirty filters can restrict air flow moving through your heating or cooling unit. This results in your HVAC unit running more often to make up for the lack of air flow. The Department of Energy indicates that a dirty furnace filter can increase HVAC energy consumption by 10 to 15 percent, and with heating and cooling accounting for half a home’s energy usage that will increase energy costs.

It is also important to remember that air filters protect your HVAC system from dust and other particles that can cause your system to work harder if it becomes plugged. Keeping the filters changed can extend the life of one of the most expensive components of your home. 

The question of filter quality gets a little more complicated because it gets into air quality concerns. Most any quality filter protects your HVAC system and keeps energy costs lower as long as you change them regularly. However, different filters protect against different particles. Take a look at the graphic provided and the Minimum Efficiency Reporting Value (MERV) rating of the filters. MERV ratings are relatively simple to understand. Higher MERV ratings mean smaller filter holes allowing less through. These are typically higher in cost. A lower MERV rating is still a great filter, but it has bigger holes and can be cheaper to purchase but not catch all things. 

Higher MERV rated filters do have the smaller holes, but manufacturers have found a workaround to keep them from clogging quicker. They add pleats to filters, and this adds more surface area for air to pass through. 

Many of the lower number MERV filters are flat with no pleats while higher and more expensive MERV rated filters have even more pleats. 

I also want to point out that not all filters display a MERV rating. Brands like 3M use a micro-particle performance (MPR) rating instead. Home Depot uses a filter performance rating (FPR). On every filter, numbers go up as expense goes up. 

As to which filter to buy? That decision is unique to your family, home, and HVAC system or manufacturer specifications. Your system may recommend a specific filter or indicate a range of filter ratings that are acceptable. Always defer to the manufacturer’s recommendations. There may also be other factors to consider. If you live on the north side of a dusty county road, then perhaps you would want to consider cheaper filters that need to replaced more often. Alternatively, maybe you have someone in the house that needs allergens filtered from the air. Don’t be afraid to mix and match depending on seasons. Perhaps a cheaper filter works for some parts of the year, but during allergy season you may need a more expensive filter. It depends on your needs.